1. Field of the Invention
The present invention relates to mobile telephone networks.
2. Description of the Related Art
FIG. 1 is a block diagram of a currently proposed GSM/GPRS or UMTS network. Each mobile operator has a domain 2 which is connected to transmit and receive signals data to and from the public switched network (PSTB) 4 and the Internet 6.
A domain typically consists of a plurality of nodes 8 (commonly known as node B's) distributed over a region through which a plurality of user equipments (UE's) such as mobile telephones 10 are located or travel through. Each node 8 can connect with a mobile UE 10 in its viscinity.
The nodes 8 are connected to a radio network controller 14 (RNC). The RNC 14 is connected to a mobile switching center 12 (MSC) and a servicing GPR support node 16 (SGSN). The RNC 14 directs non-packet data to the MSC 12 while the RNC directs packet data to the SGSN 16. The MSC 12 is connected to the PSTN and the SGSN is connected to a gateway GPRS support node 20 (GGSN).
Data relating to the caller or subscriber is held in a home location register 18 (HLR) which the SGSN 16 and the MSC 12 is able to access. The HLR 18 holds all the subscriber details to enable verification and billing and list all the subscriber service requirements. For access to the Internet, the user attaches to the SGSN and activates a packet data control (PDP) context.
Once the SGSN has accessed the HLR 18, obtained the data needed and performed the necessary checks, it will connect with the gateway GPRS support node 20 (GGSN) which will perform the final link in connecting the subscriber of each mobile UE 10 with the Internet 6.
Where voice services are required, the GGSN will connect to a voice service box 22 (VSB). Because the VSB may lie outside the mobile UE operators domain 2, it must have access to its own home location register 24 (HLR) with which the user has subscribed so that it can provide the necessary services. Thus, the VSB 22 determines from the HLR 24 the subscriber requirements eg voice mail, call waiting, call forwarding and call charging regime so that the subscriber receives his requested services and is billed accordingly depending upon such factors as the ultimate location of his target subscriber.
Each mobile UE 10 is capable of using packet domain control protocols in order to set up bearers to the VSB 22.
This mode of operation, where voice services are provided transparently within the PLMN, has several limitations. The VSB 22, while knowing the subscriber identity, does not know his location since this can only be determined within the domain 2 and so services such as free local calls cannot be processed. Also, police security checks cannot be made to trace the location of the caller from outside the location of the domain.
Secondly, the current architecture potentially requires that two sets of subscriber data be held at two physically different places and which may be owned by different proprietors. If a common HLR is used for holding of the entire subscriber data, an extra signalling load is imposed on this network element. Additionally, the call stale control function (CSCF) (which is part of the VSB) may require that an additional mechanism is used to authenticate the user.
Thirdly, the current transparent model may potentially have a problem if serving RNC (SRNS) relocation happens in the middle of a call. This can result in a break in transmission which can lead to a lowering of perceived quality of the voice service. Additionally, if the call is required to be relocated to a circuit switched (CS) only network, a multitude of problems arise eg how to signal to the CSCF to start acting as an MSC anchoring the call, how to tear down existing sessions, etc.
Fourthly, for terminating voice calls to be supported, a packet data protocol (PDP) context is required to be maintained between the UE, SGSN and GGSN. This can impose an overhead on the network elements, and (potentially) over the radio interface. The alternative approach of having a statically assigned Internet protocol (IP) address, and using the network initiated PDP context activation procedure would lead to an increase in the delay for terminating calls, and could lead to address shortage problems in the future.
These problems are solved with the network shown in FIG. 2 in which parts similar to those in FIG. 1 are similarly referenced but with the suffix A.